1. Field of the Invention
The present invention relates to a rolling element interference preventer for a guide device, such as a linear guide device having an continuous circulation path for rolling elements, a swing bearing, a ball screw, and a spline. The rolling element interference preventer prevents the rolling elements rolling at regular intervals within the continuous circulation path formed between a pair of bearing races from interfering with each other.
2. Description of the Related Art
In various rolling guide devices having a bearing, a linear motion or rotation of a pair of bearing races is enabled by use of the rolling motion of rolling elements consisting of balls or rollers carried between the bearing races. To reduce the frictional resistance by avoiding the contact between each rolling element and to produce the smooth motion by arranging each rolling element at predetermined position, it is common practice that a number of rolling elements are incorporated between bearing races, using a metallic retainer.
In the conventional guide device using the metallic retainer, since a cage has a number of pockets and rolling elements are put rotatably into these pockets, there is an advantage that the operation of incorporating a number of rolling elements into the guide device is facilitated. However, it is required to hold a number of rolling elements incorporated into the pockets of the cage not to fall off, resulting in a problem that it takes a lot of time to fabricate the cage itself.
Thus, to solve this problem, a ball interference preventer (rolling element interference preventer) for use in a guide device to prevent interference between each ball has been proposed. The endless guide device includes a track rail having a rolling path, a sliding board having a rolling groove mutually opposed to the rolling path and moving along the track rail, and a number of balls (rolling elements). With a load applied, the balls roll in a continuous circulation path formed between the rolling path of the track rail and the rolling groove of the sliding board. The ball interference preventer is composed of a flexible resin connector having an interposing portion interposed between each ball and a connecting portion for connecting between the interposing portions, and holding each ball in an arranged state and rollably. Thereby, many appreciable results were achieved including 1) attaining low noise and good sound quality by removing the metallic sound due to collision between the balls (low noise), 2) reducing the wear of ball and increasing the retention of grease (maintenance free for long term), 3) attaining excellent high speed by decreasing the relative friction velocity (high speed), and 4) smoothing the motion by greatly reducing the rolling fluctuation (sliding property) (JP-B-6-56181, JP-A-5-52217, JP-A-5-126149, JP-A-5-196036, JP-A-5-196037, and JP-A-9-14264).
By the way, thus structured ball interference preventer composed of the resin connector is immersed in, or subjected to grease, lubricating oil, or coolant in the environment where the preventer is incorporated in the circulation path for the rolling guide device. Also, the ball interference preventer undergoes actions such as bending, tension, compression, twisting, or contact friction with the ball at any time. When reciprocated in the circulation path at high speed, this ball interference preventer undergoes an operation of bending, tension and compression severely and repeatedly. Further, when the ball interference preventer composed of the resin connector is immersed in, or subjected to grease, lubricating oil, or coolant, it absorbs water and oil to swell, causing a circulation failure in the circulation path and ablation of the preventer, and degrading the durability, sliding property and wear resistance.
Therefore, the rolling element interference preventer composed of the resin connector is required to have the excellent chemical strength of oil resistance, water resistance, and chemical resistance to the grease, lubricating oil and coolant, in addition to the mechanical strength of durability, sliding property and wear resistance. In view of the life of the guide device, it is required to be so durable and resistant to wear as to run about 30,000 km or more, with small sliding resistance variation, as well as resistant to oil, water and chemicals.
Moreover, the rolling element interference preventer composed of the resin connector was not too problematical in that an unnatural load was applied only on a part of the resin connector during the use, because the minimum radius of curvature for the continuous circulation path formed in the guide device was relatively large, the ball was employed as the rolling element, and the shape of the resin connector was devised. In recent years, however, the guide device is demanded for smaller size and higher speed, and the roller is employed as the rolling element, resulting in a problem that the durability, wear resistance and sliding property may be impaired.
The present inventors made researches to attain more excellent durability and wear resistance without impairing various features (low noise, maintenance free for long term, high speed, and sliding property) of the rolling element interference preventer, especially when subjected to severe and repetitive actions of bending, tension and compression, and found that the rolling element interference preventer should be produced using a thermoplastic resin elastomer having specific balance (relation) for a 10% elongation stress, a tensile stress and a bending modulus of elasticity to achieve the aim, thus completing this invention.
Accordingly, it is an object of the invention to provide a rolling element interference preventer for a guide device, which prevents a number of rolling elements rolling at regular intervals in a continuous circulation path of the guide device from interfering with each other. The rolling element interference preventer is not only excellent in low noise, maintenance free for long term, high speed and sliding property, but also excellent in durability and wear resistance, and can be used stably over the long term.
The present invention provides a rolling element interference preventer for a guide device to prevent a number of rolling elements rolling at regular intervals in a continuous circulation path of the guide device from interfering with each other, wherein the rolling element interference preventer is formed of a thermoplastic resin elastomer having a physical property in accordance with an expression, (Axc3x97B)÷Cxe2x89xa718, where A is a 10% elongation stress, B is a tensile strength, and C is a bending modulus of elasticity.
As the thermoplastic resin elastomer, polyamide resin elastomer, polyester resin elastomer, polyurethane resin elastomer, styrene resin elastomer, and olefine resin elastomer are exemplified. They should be highly resistant to oil, water and chemicals in the service environment of the rolling guide device, especially in the service environment where the guide device is immersed in, or subjected to grease, lubricating oil, or coolant. The coefficient of water absorption measured in the environment of equilibrium moisture percentage 23xc2x0 C., 65% RH is 1.5 wt % (% by weight) or less, and preferably 0.5 wt % or less. The swelling factor measured in an immersion test of chemical at a temperature of 85xc2x0 C. for 672 hours is 3% or less. Furthermore, the tensile strength retention in an immersion test of boiling water at 100xc2x0 C. is 70% or more after ten days, and preferably 80% or more.
In this invention, the thermoplastic resin elastomers satisfying a physical property in accordance with the expression, (Axc3x97B)÷Cxe2x89xa718 (A: 10% elongation stress, B: tensile strength, and C: bending modulus of elasticity) are employed. Though slightly different depending on the type of the rolling guide device and whether the rolling element is a ball or a roller, the 10% elongation stress A is from 60 to 200 kgf/cm2, and preferably from 90 to 160 kgf/cm2, the tensile strength B is from 340 to 460 kgf/cm2, and preferably from 360 to 430 kgf/cm2, and the bending modulus of elasticity C is from 1000 to 5000 kgf/cm2, and preferably from 1200 to 2700 kgf/cm2.
If the 10% elongation stress of the thermoplastic resin elastomer is not less than 60 kgf/cm2, the shape of the rolling element interference preventer is maintained against a centrifugal force acting on the rolling element of the guide device in the fast operation, resulting in that the sliding resistance decreases in the continuous circulation path of the guide device. On the contrary, if it is not more than 200 kgf/cm2, a problem of flexure fatigue failure is prevented. If the tensile strength is not less than 340 kgf/cm2, the durability is increased, or conversely if it is not more than 460 kgf/cm2, the problem of flexure fatigue failure is prevented. Moreover, if the bending modulus of elasticity is not less than 1000 kgf/cm2 and not more than 5000 kgf/cm2, the sliding property is increased.
Herein, it is needed that the guide device for use with the rolling element interference preventer of the invention has a pair of bearing races, and the continuous circulation path for the rolling elements rolling with a load applied between the pair of bearing races, and the guide device may be a linear guide device for endless track, a swing bearing, a ball screw, and a spline, for example.
And the rolling element interference preventer of this invention can take various forms, depending on the type of guide device to which it is applied. For example, in a case where the guide device is a linear guide device for endless track having a track rail (one bearing race) having a rolling path, a sliding board (other bearing race) having a rolling groove mutually opposed to the rolling path and moving along the track rail, and a number of rolling elements rolling with a load applied between the rolling path of the track rail and the rolling groove of the sliding board, it is preferred that the rolling element interference preventer consists of a flexible resin connector having an interposing portion interposed between each rolling elements, and a connecting portion for connecting each interposing portions, and preferably can hold a number of rolling elements rollably by the interposing portions and the connecting portion.
Moreover, in the case where the rolling element interference preventer is made up of this flexible resin connector, the resin connector may be provided with a chamfer guide portion at either terminal end to guide the top end portion of the resin connector, whereby when the guide device is moved in the continuous circulation path, especially when the top end portion of the rolling element interference preventer enters a direction converting path of the circulation path, or exits from the direction converting path, the top end portion is guided to move the guide device smoothly. By forming the chamfer guide portion at either terminal end of the resin connector, the rolling element interference preventer can be guided smoothly in any of forward and backward directions in the reciprocating motion of the guide device.
The length of the rolling element interference preventer to be molded is decided in consideration of the length of the circulation path for the guide device using it. However, if the guide device is increased in size and the length of circulation path is great, the rolling element interference preventer may be divided into two or three for molding, whereby the size of mold can be reduced. In this case, each resin connector constituting each of two or three parts divided from the rolling element interference preventer is formed with a chamfer guide portion at either terminal end.
In the case where the rolling element interference preventer of the invention is applied to the linear guide device for endless track, if the rolling elements are balls, the thermoplastic resin elastomer forming the resin connector has the properties that the 10% elongation stress A is from 60 to 150 kgf/cm2, and preferably from 90 to 130 kgf/cm2, the tensile strength B is from 340 to 400 kgf/cm2, and preferably from 350 to 380 kgf/cm2, and the bending modulus of elasticity C is from 1000 to 2000 kgf/cm2, and preferably from 1200 to 1800 kgf/cm2. By employing the values in the above ranges for the 10% elongation stress A, tensile strength B and bending modulus of elasticity C, the ball interference preventer can exhibit the excellent and balanced performances (low noise, maintenance free for long term, high speed, sliding property, durability and wear resistance).
In the case where the rolling element interference preventer of this invention is applied to the linear guide device for endless track, if the rolling elements are rollers, the thermoplastic resin elastomer forming the resin connector has the properties that the 10% elongation stress A is from 80 to 200 kgf/cm2, and preferably from 100 to 160 kgf/cm2, the tensile strength B is from 380 to 460 kgf/cm2, and preferably from 430 to 460 kgf/cm2, and the bending modulus of elasticity C is from 1500 to 5000 kgf/cm2, and preferably from 2000 to 4000 kgf/cm2. By employing the values in the above ranges for the 10% elongation stress A, tensile strength B and bending modulus of elasticity C, the roller interference preventer can exhibit the excellent and balanced performances (low noise, maintenance free for long term, high speed, sliding property, durability and wear resistance).
Moreover, in the case where the guide device is a ball screw having a screw axis (one bearing race) with a helical rolling path for a ball, a nut (other bearing race) with a helical rolling groove mutually opposed to the helical rolling path, and a number of balls rolling with a load applied between the helical rolling path of the screw axis and the helical rolling groove of the nut, the ball interference preventer may be the resin connector like that of the linear guide device for endless track, or a spacer interposed between each balls.
The rolling element interference preventer of this invention can be produced by conventional well-known methods, using the thermoplastic resin elastomer as described above. For example, in a case where the rolling element interference preventer is made up of the resin connector, a number of rolling elements can be produced as a core by injection molding or a so-called insert molding (as described in JP-A-6-56181, JP-A-5-52217, JP-A-5-126149, JP-A-5-196036, JP-A-5-196037, and JP-A-9-14264), or other methods.